Centrifuge with a sieve system and method for operating the same

ABSTRACT

The invention relates to a centrifuge, especially a separator, with a feed tube ( 3 ) and/or a distributor ( 5 ) for feeding a material to be centrifuged into a centrifuge compartment ( 9 ) that is defined by a centrifugal drum ( 7 ) and in which a sieve system is disposed. The invention is further characterized in that the sieve system is designed and disposed in such a manner that the flow direction of the material to be centrifuged emerging from the distributor ( 5 ) and the flow direction of particles deposited on the sieve elements of the sieve system is identical. The invention further relates to a method for cleaning the centrifuge, according to which preferably a piston slide valve of the centrifuge is opened so that a return flow of liquid through the sieve system removes substances baked to the sieves and/or any impurities.

[0001] The invention relates to a centrifuge, particularly a separator, according to the preamble of claim 1, and to a method for its operation.

[0002] A centrifuge of the above-mentioned type and a method for its operation are known from German Patent Document DE 25 29 614 C2. This document describes a device for the continuous rotary pressure filtration of liquid media. Filtration in the sense of this document are sieve as well as membrane filtrations as well as micro- or ultrafiltrations. By means of a hydrostatic pressure difference, a concentrate current component is generated parallel to the surface of the filter, for the purpose of which a hydrodynamic delivery pressure is generated in the ring gap between the centrifuge drum and the coaxial drum-shaped filter element in that the drum and the filter element are simultaneously acted upon by mutually different rotary frequencies. Without the independent relative rotatability, allegedly an extremely surface-laminar cross-current component would be created between the filters which has only so little effect that the fractionation process would already cease shortly after the start of the filtration as a result of polarization effects and pore sealing.

[0003] The separate rotatability of the sieve drum causes high constructive expenditures and therefore considerably increases the cost of the centrifuge. For this reason, among others, the above described solution has not been successful according to a finding of the invention.

[0004] It should also be noted that, despite the relative rotatability of the sieve drum with respect to the centrifugal drum, a rerinsing of the membrane by means of a rinsing liquid is often required. However, such a rerinsing requires high expenditures and interrupts the centrifuging operation for a considerable period of time.

[0005] It is an object of the invention to further develop the initially described centrifuge such that a constructively simple sieve system is provided in the case of which solids can easily flow out of the sieve area and the pore sealing is reduced. In addition, an advantageous method of cleaning the centrifuge is to be obtained.

[0006] With respect to the centrifuge, the invention solves this task by means of the object of claim 1 and, with respect to the method, by means of the object of claim 21.

[0007] Advantageous further developments of the invention are contained in the subclaims.

[0008] Thus, the sieve system is designed and arranged such that the flow direction of the material to be centrifuged emerging from the distributor and the flow direction of particles deposited on the sieve elements of the sieve system is identical. This results in advantages with respect to the disturbance-free transport which must not take place against a flow, as is the case in the different other constructions. A separate rotatability of the sieve system relative to the drum, as in the state of the art of the above-mentioned type, is also no longer required.

[0009] For example, the sieve system comprises at least one—but preferably several—sieve plate(s) which is/are arranged essentially radially with respect to the feed tube and/or the distributor and may be designed as a membrane plate made of a ceramic material. As a result of the flow direction of the centrifuged or charged material between the membrane plates (or at the exterior sides of the outermost membrane plate) toward the outside, the flow direction with the solids deposited on the membrane, whose transport takes place toward the outside because of the centrifugal effect, is identical.

[0010] A piston slide valve for closing the centrifugal drum is preferably provided and/or a solids-enriched stage is drained from a solids space of the centrifugal drum by way of openings—preferably nozzles—in the outside diameter of the solids space and/or by way of ducts/bores toward the centrifugal drum head. Concerning such a draining by means of nozzles at the piston slide valve, reference is made to German Patent Document DE 22 14 487.

[0011] For the cleaning as well as for the draining, the solids space centrifuge compartment is opened up—particularly by opening the piston slide valve—so that solids deposited and/or disposed on the sieve and/or impurities (and possibly also cloggings, baked-on substances) are drained through the opening(s) (opened up by the piston slide valve).

[0012] This cleaning has the advantage that it can be carried out without any additional use of rinsing liquid and a rinsing by means of a rinsing liquid is required only after a relatively long operation.

[0013] It should be stressed that, because of modern control techniques, it is possible to very precisely control the evacuation mechanism and in this manner also control the cleaning effects in the desired fashion. As a result, a long service life of the membrane insert is achieved without the requirement of a production stop because of clogging. Because of the speed of the evacuating mechanism and the permitted regulating of the discharge volume, the intensity of the cleaning effect can be controlled as a function of the product.

[0014] As another variant of the invention, the draining of the concentrate is conceivable by way of a separating plate or small tube, ducts and nozzles outside the membrane insert. As a function of the product, this may result in a lengthening of the rerinsing intervals (evacuation intervals). An automating of the evacuation point in time is also possible by monitoring the stage drained there.

[0015] As another alternative, the carrying-away of a partial flow of the concentrate by way of nozzles is conceivable.

[0016] Instead of a piston slide valve, an analog operating, discontinuously working opening mechanism may be used.

[0017] The membrane plates may be mounted in the centrifugal drum individually as well as as a preassembled unit. This naturally offers advantages during the mounting/demounting.

[0018] In particular, the invention combines in a simple manner the technology of modern piston slide valve separators known per se with the idea of a membrane plate insert and thereby creates a type of “membrane separator”.

[0019] The solids collection space preferably has a double-cone shape.

[0020] In particular, the invention provides a method of cleaning a centrifuge according to the invention in the case of which, for cleaning the sieve, preferably a piston slide valve of the centrifuge is opened up, so that a return flow of liquid through the sieve removes substances baked to the sieve and/or impurities of the sieve.

[0021] In the following, the invention will be described in detail by means of an embodiment with reference to the drawing.

[0022]FIG. 1 is a sectional view of a centrifuge according to the invention;

[0023]FIGS. 2a and 2 b are two sectional views of the area of the membrane plate sieves offset with respect to one another at an angle.

[0024]FIG. 1 shows a separator with a feed tube 3 which leads into a distributor 5 used for the introduction of a material to be centrifuged into a centrifuge compartment 9 bounded by a centrifugal drum and designed in the shape of a double cone, which centrifuge compartment 9 is provided with a sieve system 11—also called membrane insert—made of a ceramic material.

[0025] According to FIG. 1, the sieve arrangement 11 is formed of three membrane plates 13 spaced axially from one another and extending radially to the feed tube 3 and the distributor 5. FIGS. 2a and 2 b show the membrane plates which are each arranged on spacing rings 15 which surround the distributor 5 and consist of two membrane disks 13 a, 13 b which are axially spaced away from one another and, in each case, in the area of their outer circumference, are connected with one another by way of a spacing ring 17. Ring gaps 19 are formed between the membrane plates 13. The membrane disks 13 a, 13 b are each stabilized on the mutually facing sides of each membrane plate 13 by means of supporting rings 21.

[0026] Purely as an example, according to FIG. 1, three membrane plates 13 are provided in the present case. However, FIG. 2 shows that a larger number of membrane plates may also be provided when the distributor 5 of the separator 1 is designed correspondingly.

[0027] In its wall 23, the distributor 5 has radially aligned bores 25 which lead into at least one duct 27 which extends vertically to the distributor 5 on its outer circumference and, in turn, by way of bores/ducts 29, leads between the spacing rings 15 into the ring gaps 19 between the membrane plates 13. Seals 30, such as O-rings, flat packings, are situated between the spacing rings 15. It is also possible to lay the spacing rings 15 directly upon one another without seals and produce a metallic tightness.

[0028] According to the sectional view of FIG. 2b, which is angularly offset with respect to FIG. 2a, the spacing rings 15 are also provided with drain ducts 31 which extend upward at an angle with respect to the membrane plates 13 and which connect the ring space 33 between two mutually associated membrane disks 13, 13 b of the membrane plates 13 which a drain duct 35 for liquid constructed vertically in the spacing rings 15. The spacing rings 15 are sealed off relative to one another by means of seals 30. The ducts 31, 35 are constructed in a hydraulically separated manner with respect to the feed ducts 29.

[0029] In the area of the interior wall of the centrifugal drum 7, a draining system 37 may be arranged for draining the more solid but still free-flowing stage.

[0030] Piston slide valves 39, which are known per se, in addition, permit the carrying-away of solids from the drum through radially outward leading bores 41 or slits in the centrifugal drum 7.

[0031] The operation of this system is as follows.

[0032] The material to be centrifuged enters through the feed tube 3 and the distributor 5 and its bores 25 into the duct 27 and through the bores/ducts 29 between the spacing rings 15 into the ring gaps 19 between the membrane plates 13.

[0033] From here, the material to be centrifuged flows radially toward the outside, a portion of the material to be centrifuged entering the membrane plates 13 so that a portion of the material to be centrifuged is clarified in the membrane plate area (arrows P). This portion of the liquid stage is drained through the ducts 31 and 35.

[0034] The residual fraction of the material to be centrifuged (solids) emerges radially toward the outside from the membrane plates 13 and passes beyond the plate spacing rings into the centrifuge compartment 9. As a result of the above-described draining systems, the solids stage can be carried away as a function of the product. As a result of the flow direction of the centrifuged and charged material between the membrane plates (or at the exterior sides of the outermost membrane plate) toward the outside, the flow direction with the solids deposited on the membrane toward the outside is identical (arrow F).

[0035] When the piston slide valve 39 is opened, the solids are guided from the solids collection space to the outside. In this case, a strong flow also occurs from the intermediate spaces 33 of the membrane plates toward the outside, whereby solids deposited on the membrane plates 13 are removed and are also guided to the outside through the piston slide valve openings 41.

[0036] The flow conditions are illustrated by arrows P as well as A (carrying away of solids stage), F (flow direction), E (evacuation stage) and Z (feed).

List of Reference Numbers

[0037] separator 1

[0038] feed tube 3

[0039] distributor 5

[0040] centrifugal drum 7

[0041] centrifuge compartment 9

[0042] sieve system 11

[0043] membrane plate 13

[0044] spacing ring 15

[0045] spacing ring 17

[0046] ring gaps 19

[0047] supporting rings 21

[0048] wall 23

[0049] bores 25

[0050] duct 27

[0051] bores/ducts 29

[0052] seals 30

[0053] drain ducts 31

[0054] ring space 33

[0055] drain duct 35

[0056] draining system 37

[0057] piston slide valve 39

[0058] bores 41

[0059] arrow (feed) Z

[0060] arrow (draining solids stage) A

[0061] arrow (flow direction) F

[0062] arrow (evacuation stage) E

[0063] arrow P 

1. Centrifuge, particularly a separator, a) having a feed tube (3) and/or a distributor (5) for introducing a material to be centrifuged into a sieve system (11) which is arranged in a centrifuge compartment (9) bounded by a centrifugal drum (7), b) the sieve system (11) is designed and arranged such that the flow direction of the material to be centrifuged emerging from the distributor (5) and the flow direction of particles deposited on sieve elements of the sieve system is identical, c) the sieve system having a plurality of axially mutually offset sieve plates (13) and the sieve plates being arranged essentially radially with respect to the feed tube (3) and/or the distributor (5), characterized in that d) a piston slide valve (39) is provided for closing the centrifugal drum (7), e) the sieve plates are designed as membrane plates (13) which have at least two axially spaced membrane disks (13 a, 13 b), f) the membrane disks (13 a, 13 b) each being connected with one another by way of at least one spacing ring (15) in the area of their outer circumference.
 2. Centrifuge according to claim 1, characterized in that the membrane plates (13) consist of a ceramic material.
 3. Centrifuge according to claim 1 or 2, characterized in that the membrane disks (13 a, 13 b) are connected with one another in the area of their inside diameter by way of at least one spacing ring (17).
 4. Centrifuge according to one of the preceding claims, characterized in that ring gaps (19) are formed between the membrane plates (13).
 5. Centrifuge according to one of the preceding claims, characterized in that the spacing rings (15) situated on the inside diameter have bores (31, 35) for draining clarified liquid.
 6. Centrifuge according to one of the preceding claims, characterized in that the spacing rings (15) situated on the inside diameter have ducts (29) for feeding the charged material between the membrane plates (13).
 7. Centrifuge according to one of the preceding claims, characterized in that the spacing rings (15) situated on the inside diameter are disposed directly above one another without any sealing.
 8. Centrifuge according to one of claims 1 to 6, characterized in that seals (30) are arranged between the spacing rings (15) situated on the inside diameter.
 9. Centrifuge according to claim 8, characterized in that the seals (30) arranged between the spacing rings (15) situated on the inside diameter are flat packings or O-rings.
 10. Centrifuge according to one of the preceding claims, characterized in that the distributor (2) has bores (25) in its wall (23), which bores (25) lead directly or by way of additional bores/ducts (29) into the ring gaps (19) between the membrane plates (13).
 11. Centrifuge according to one of the preceding claims, characterized in that the spacing rings (15) situated on the inside diameter are provided with drain ducts (31) which connect a ring space (33) between the membrane disks (13 a, 13 b) of the membrane plates (13) with a draining system (37) for draining the liquid stage.
 12. Centrifuge according to one of the preceding Claims, characterized in that the drain ducts (31, 35) are constructed in a hydraulically separate manner with respect to the feed ducts (29).
 13. Centrifuge according to one of the preceding claims, characterized in that a solids-enriched stage can be discontinuously drained from a solids space (9) of the centrifugal drum (7) by way of openings (41) in the piston slide valve (39) by opening the piston slide valves and/or is continuously drained by way of ducts (37)/ bores or nozzles in the exterior area of the centrifuge compartment (9).
 14. Centrifuge according to one of the preceding claims, characterized in that the openings (41) in the piston slide valve (39) have a nozzle-type design.
 15. Centrifuge according to one of the preceding claims, characterized in that the membrane plates (13) are constructed individually or as several plates (13) as a preassembled unit and are inserted into the centrifugal drum (7).
 16. Method of cleaning a centrifuge according to one of the preceding claims, characterized in that, for cleaning the sieve system, preferably a piston slide valve of the centrifuge is opened up so that a return flow of liquid through the sieve system removes substances baked to the sieve system and/or impurities from the latter.
 17. Method of cleaning a centrifuge according to one of the preceding claims, characterized in that, for cleaning the sieve system, a piston slide valve of the centrifuge is opened up so that a return flow of liquid through the sieve system removes substances baked to the sieve system and/or impurities from the latter. 